Encyclopaedia Britannica (《大英百科全书》) used to be the king of encyclopaedias. It hopes to become the most important encyclopaedia again.

    1     It moved to Chicago in 1935. In 1990, the company sold more than 100,000 sets of books.     2     Book sales dropped during the time of the Internet because people stopped getting information only from books.     3    

Some online encyclopedias started in the early 21st century. It was the beginning of the end of Encyclopaedia Britannica books. Several years ago, the company stopped publishing the books. It put the whole encyclopaedia on the Internet.     4     One reason is that some online encyclopeadias have millions of articles, but Britannica has only 106,000. About half of Britannica’s articles are free while almost all of the articles on other online encyclopaedias are free.

Still, some readers believe that Britannica’s articles are more trustworthy (值得信任的).     5     They make sure the articles are correct. The president of Britannica has a plan. He wants to offer all of the encyclopaedia online for free. The company hopes more people will read it.

【推荐2】Do you know the reason why we feel tired in the middle of a class? Maybe you would say it is because the teacher’s class is boring. However, the real reason is probably that we don’t have enough sleep. Perhaps this is something you have not paid enough attention to.

Why do we need sleep? Sleep helps our body heal, grow, and stay healthy. It also gives us energy, so we can be active all day. Doctors and health scientists say when you close your eyes and need to rest, sleep is just the best! This is more than advice.

Enough sleep is important to us. How much sleep do we need? New-born babies sleep most of the time. They can sleep 20 to 22 hours a day. Children need 10 to 12 hours of sleep a day. Teenagers need 8 to 10 hours of sleep a day because they need lots of energy to grow into their adult bodies. Grown-ups usually need 6 to 8 hours of sleep to keep active.

Almost everyone has their dreams while they sleep, but not all of them can tell their dreams clearly when they wake up. Some people talk in their dreams. More surprisingly, some may even get up in their dreams and walk around. This is called “sleepwalking”. Are you a sleepwalker? Or, is there a sleepwalker around you?

It’s not just people that love to snooze (打盹). In fact, many animals have unusual or surprising sleeping habits. Some animals, such as bears and hedgehogs (刺猬), sleep all through winter. The swift (雨燕) is a special bird that can sleep while it flies! Cute koalas sleep around 18 hours a day. Giraffes don’t need much sleep. They usually sleep standing up.

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【推荐3】Being a teenager can be challenging, but it can also be exciting. You’re becoming more independent and making decisions for yourself. You are also learning to take risks and solve problems better. And changes are happening throughout your body, even in your brain.

The changes in your brain are influencing how you develop into an adult. Imagine the structure（结构）of your brain is like a big road map. Lots of roads lead to different destinations（目的地）. When you were a child, as you learnt new things, your brain created more and more roads to different destinations. By the time you become a teenager, many different roads lead to the most important places on the map. Now your brain's job is to make that map more efficient.

As a result, your experiences as a teenager actually influence the way that your brain develops. If you spend hours playing video games, what skills do you use? You learn to see something with your eyes and respond to it with your hands. As you develop those skills, your brain is making sure that the roads leading to them are especially fast and efficient. So, your video-game playing could be preparing you for a career such as a pilot.

This is a great time for you to practice new skills and discover what you're good at and try what you love doing. Go out and try different activities, and stick to them if you think they’re useful. Remember that with everything you do, you’re shaping your brain for the future.

【推荐2】Feeling stressed has almost become the norm(常态) for many busy American families. Although one kind of stress called 'eustress' can actually be positive( 积极的 ) and productive(有用的), many suffer far too often from negative stress. All that stress leads us to cope in unhealthy ways that take their toll on( 对 …… 造成伤害 ) overall health and well-being. Unfortunately, stress is not just a problem for adults. Teens are also vulnerable(易受伤害的) to stress and its effects.

The latest Stress in America Survey by the American Psychological Association (APA) polled(对……做民意调查) adults as well as 1,018 teens who live in the United States about stress over the previous month. While American adults report higher stress levels than what they believe to be healthy, the survey also shows the patterns of unhealthy stress behaviors we see in adults impact(影响) teens as well. According to the survey, many American teens report experiencing stress at unhealthy levels, appear uncertain in their stress management techniques and experience symptoms(症状) of stress in numbers that mirror adults' experiences. Stress during the teen years also seems to take a toll on activity, nutrition and lifestyle behaviors.

Stress impacts teens in many ways. The survey shows that 36% of teens report fatigue(feeling tired); 35% report lying awake at night; 32% report having headaches; and 23% report skipping a meal.

The report also shows that teens are less aware(有……的意识) than adults about the impact stress can have on their physical and mental health.

It's important that parents find ways to manage stress positively and productively. Because our kids see what we do and how we handle different situations and stressors, for better or worse, we need to model as best as we can positive ways of perceiving(认识) and coping with stress.

Staying physically active, engaging in exercise and sitting less can temper(缓和) stress. Finding activities we enjoy can help our hearts be healthier. Eating different kinds of nutrient-rich foods, for example, whole grains, fruits, vegetables and healthy fats throughout the day can help have mood-boosting. Connecting with others regularly, laughing and thinking can also help. Getting enough sleep by having regular bedtimes can also help us avoid fatigue.

【推荐3】It is widely agreed that the over-use of fossil fuels, such as coal and oil has caused serious environmental problems. Scientists are trying to find new clean energies that do not pollute the air, the water or the ground. Solar power is one of them.

Solar power is a kind of electricity which is produced by taking energy from the sun, using solar panels. The power is easy to get and will never be used up. Whenever it is sunny, there is the power. The power is clean and renewable. It helps to reduce waste and pollution, which is great for the environment. In the areas that are too far away to send electricity to or not easy to build electric power plants, solar power is especially necessary. It enables the people there to use lights, TVs, computers, washing machines, fridges and many other things.

Therefore, more and more countries, such as China, the USA, Japan and India, encourage scientists to develop practical technology to put solar power to use. However, the power is not as widely used as expected.

One of the challenges is that a solar power system: needs sunshine. Countries or areas with a lot of rain, like the UK, are not suitable to develop such power systems. Secondly, a solar power plant requires a very large site to fix enough solar panels to collect sunlight and change it into electricity. Maybe an area in the desert would be one of the perfect places for such a plant to build. What’s more, solar panels are expensive at present though the energy itself doesn’t cost anything.

Today scientists are working hard to develop more practical and cheaper solar power systems. Maybe one day solar power will be one of the most important clean energies in our life.